6-fluoro-3-hydroxy-2-pyrazinecarboxamide (hereinafter referred to as T-705) is a compound which is useful for the prevention and treatment of viral infectious diseases, particularly influenza viral infectious diseases. It is known that T-705 can be produced from, for instance, 6-fluoro-3-hydroxy-2-pyrazinecarbonitrile (PATENT DOCUMENT 1).
As a process for producing 6-fluoro-3-hydroxy-2-pyrazinecarbonitrile, for instance, the following (1) and (2) processes are known: (1) a process in which 3,6-difluoro-2-pyrazinecarbonitrile is reacted with benzyl alcohol and the reaction product is debenzylated; and (2) a process in which 3,6-difluoro-2-pyrazinecarbonitrile is subjected to a reaction with water (PATENT DOCUMENT 1).
These known processes, however, have some disadvantages, for example, those as mentioned below: (A) the intermediate product 3-benzyloxy-6-fluoro-2-pyrazinecarbonitrile is a labile compound; (B) troublesome operations such as extraction, column chromatography and removal of the solvent by distillation are necessary; (C) harmful hydrogen fluoride is generated when the reaction mixture is acidified; and (D) the yield is low.
Further, it is not easy to isolate 6-fluoro-3-hydroxy-2-pyradinecarbonitrile from a reaction mixture in a high yield by a simple operation because this compound is soluble in water and many organic solvents.    PATENT DOCUMENT 1: International Publication No. WO 01/60834